Butyl rubber silica composition and method of preparation



United States BUTYL RUBBER SILICA COMPOSITION AND METHOD OF PREPARATIONApplication September 27, 1954 Serial No. 458,663

10 Claims. (Cl. 260-415) No Drawing.

This invention relates to the production of silica reinforced rubbercompositions from isobutylene rubber-like polymers, includinghomopolymers and copolymers, such as butyl rubber. Prior to the presentinvention the provision of butyl rubber reinforced with siliceouspigment has been complicated by the fact that such rubbers in thevulcanized state conventionally exhibit a serious bloom. This bloommanifests itself in the form of a fine white powder on the surface ofthe rubber which is produced. While some portion of the powder can bewiped 01f, further powder appears to exude from the surface of therubber on standing. Consequently, the resulting rubber products areunsightly and the full color of the rubber is thereby impaired. This isa serious objection since the use of siliceous pigments, which areintrinsically white, permits the production of nonblack rubbercompositions which are highly desirable for commercial use. At the sametime, however, the presence of the bloom on the surface of the rubber isvery unsightly.

According to the present invention it has been found that this bloom maybe avoided in butyl rubber stocks which contain no carbon black byeffecting a vulcanization of the butyl rubber-siliceous pigmentcomposition containing a lower than normal concentration of elementalsulphur and up to about 2.5 parts by weight of a dimorpholinepolysulfide, such as 4,4 dithiodimorpholine.

The term butyl rubber is intended to include polymers of isobutylene andcopolymers of isobutylene and a diolefin of the group consisting ofbutadiene, isoprene, dimethyl butadiene, pentadiene, cyclopentadiene,and piperylene, such as are described in U. S. Patent No. 2,442,068.Such polymers normally contain 70 to 99 percent of the isobutylene and30 to 1 percent by weight of the diolefin. These copolymers are producedby a low temperature polymerization, for example, at a temperature ofsubstantially minus 95 C.

The siliceous pigments which are used in accordance with the presentinvention are finely divided pulverulent materials containing in excessof about 55 to 60 percent Si by weight on the water-free basis andhaving an average ultimate particle size below 0.1 micron, preferably inthe range of 0.01 to 0.05 micron. Typical pigments of this character arefinely divided silica, calcium silicate, magnesium silicate, sodiumaluminum silicate, sodium calcium aluminum silicate, aluminum silicate,and the like.

By far the strongest rubber compositions have been produced using finelydivided silica which contains an excess of about 85 to 90 percent SiO onthe water-free basis. Such silicas usually have a surface area in therange of about 50 to 250 square meters per gram, the best being in therangeof 90 to 225 square meters per gram. They may contain small amountsof metallic components such as CaO, A1 0 MgO, ZnO or the like, usuallyin chemical combination. Typical silica pigments f the type contemplatedare described in an application atet 2,821,516 Patent-edv Jan. 28, 1958Streams of aqueous sodium silicate solution containing grams per literof SiO as Na O(SiO and calcium chloride solution containing 100 gramsper liter of CaCl and 30 to 40 grams per liter of sodium chloride werefed directly into the central area of a centrifugal pump at 150 F.

The rates of flow were adjusted so that calcium chloride wasapproximately 10 percent in excess over the stoichiometric quantityrequired for reaction, and so that the amount of liquid supplied to thepump was about 25 percent below the output capacity of the pump. Inconsequence, the solutions were subjected to turbulent intermixing inthe pump.

The slurry of calcium silicate thus produced was introduced into a tankand sufficient hydrochloric acid solution containing 28 percent byweight of HCl was added, with stirring, to reduce the pH of the slurryto 2. Thereupon, sutlicient sodium hydroxide solution containing 40percent by weight of NaOH was added to raise the pH of the slurry to7.5. The precipitated silica was recovered by decantation andfiltration, and was dried in an oven at a drying temperature of to C.for 12 hours. The free water content of the product was within the rangeof 3 to 8 percent by weight of the pigment.

Example II An aqueous solution of sodium silicate was prepared bydiluting 5.88 liters of sodium silicate containing 298 grams per literof SiO as sodium silicate having the composition Na O (SiO withsufiicient water to produce 20.7 gallons of solution. A further solutionwas made by dissolving 1220 grams of calcium chloride and 320 grams ofsodium chloride in 16.0 gallons of water. Streams of these aqueoussolutions were fed directly into the central area of a centrifugal pump,proportioning the rates of flow so that calcium chloride remained inexcess over the stoichiometric quantity required for reaction with thesodium silicate at all times. After mixing of the two solutions wascomplete, 475 grams of ammonium chloride was added to the resultingcalcium silicate slurry and the slurry was thereafter boiled for about 4hours, at which time the odor of ammonia was very faint. Thereafter, theslurry was washed and filtered, and was dried at a temperature of about120 C. A white friable product having the following composition wasproduced:

Percent by weight Ignition loss 13.67 SiO 77.84 R 0 (iron and aluminum)1.30 CaO 5.88 MgO 1.36

Example III Twentysix hundred gallons of sodium silicate solutioncontaining 18 grams per liter of NaCl and 20 grams per liter of Na O asthe sodium silicate, Na O(SiO was placed in a 4000-gallon tank. Carbondioxide gas containing 10 percent by volume of CO the balance beingnitrogen, was introduced into the solution over a period of 3 hourswhile holding the solution at 30 C. at a rate sufiicient to react withall of the sodium silicate .and convert 2025 percent of the Na O contentthereof to bicarbonate. Thereafter, the resulting slurry was boiled forone hour, filtered, and washed. The filter cake was reslurried and asolution of Al (SO l8H O, in quantity sufficient to introduce into theslurry /2 percent of A1 based upon the weight of SiO: in the slurry, wasadded to the slurry. Thereafter, the slurry was stirred briefly andenough hydrochloric acid was added to adjust the pH to 5.7. Theresulting slurry was filtered and the filter cake dried.-

Example IV Seventeen thousand gallons of a sodium silicate solu tion isplaced in a 50,000-gallon tank. This solution contains the sodiumsilicate Na O(SiO in amount sufficient to establish an Na Oconcentration of 20.3 grams per liter. This solution contains no sodiumchloride ex cept that minor amount (less than 0.08 percent) usuallypresent in commercial sodium silicate. The solution is held at atemperature of 167 F.i. Carbon dioxide gas containing 10.0 to 10.8percent of CO the balance being nitrogen and air, is introduced into thesolution at a gas temperature of 115 to 145 F. at a rate suflicient toprovide 1250 cubic feet of the carbon dioxide gas per minute (measuredat 760 millimeters pressure and 0 C.). This gas is introduced directlyunder a turbo agitator in a manner to achieve uniform distribution ofgas, and the mixture is vigorously agitated. Carbon dioxide introductionis continued at this rate for 8 /2 hours, at which time about 120 to 140percent of the theoretical amount of CO has been introduced. After thisperiod of 8 /2 hours, the rate of introduction of carbon dioxide isreduced to 400 cubic feet per minute and the solution is boiled for 1%hours. Sixteen hundred gallons of the boiled slurry containing 6.4 gramsper liter of Na O was placed in a tank and 168 pounds of aluminumsulphate Al (SO l8H O was added. Hydrochloric acid was added to adjustthe pH of the slurry to 5.7, and the silica was recovered and dried.

The morpholine polysulfides are compositions having the followingformula:

where x is a small whole number in excess of 1 but rarely in excess of5. Of particular interest in this regard is the compound 4,4dithiodimorpholine which is manufactured and sold to the trade asSulfasan R by the Monsanto Chemical Company.

The amount of morpholine polysulfide which may be used according to thepresent invention depends to some degree upon the degree ofvulcanization desired. Usually, this amount will range between 0.5 to2.5 parts by weight per 100 parts of the butyl rubber. In conjunctionwith the morpholine polysulfide, it is necessary to use a small amount,less than that which will give a good cure and which will produce bloom,usually ranging from 0.75 to 1.5 parts by weight of elemental sulphurper 100 parts of rubber.

The amount of siliceous pigment used normally ranges from 10 to 80 partsby weight per 100 parts by weight of polyisobutylene polymer.

In the practice of the invention, the butyl rubber, the silica pigment,elemental sulphur, and morpholine polysulfide are milled together in themanner conventional for milling rubber stock. Other conventionalcomponents normally incorporated in butyl rubber stocks, such ashydrocarbon softener. accelerators, plasticizers, and the like, may bemilled into the stock at the same time or subsequently. Thereafter, themilled composition is sheeted out and used in accordance with standardaccepted procedures. vulcanization of the product is effected atconventional temperatures, for example, 300 to 350 F.

The following example is illustrative:

Example A In this example, the copolymer of isobutylene and isoprene,known as GR-I 15, was used. This is a product of the copolymerization of97.5 parts of isobutylene and 2.5 parts of isoprene prepared at a lowtemperature.

Compounds were prepared according to the following formulations Oom-Compound A pound B GR-I 15 (Butyl Rubber) 100 100 Zinc Oxide 5 5 Silicaprepared as in Example 39 39 Iron Oxide 2 2 Methyl Tuads (Tetramethylthiuramdisulfide). 2 2 Sulfun- 2 1 Snlfasan R (4,4dithiodimorphollne) 1. 5 Diethylene Glycol. .5 2. 5 Paraflin 0. 0. 75BxDO (Butoxyethyl diglycol carbonate) 1 1 Compound A which contained 2parts by weight of elemental sulphur exhibited a heavy bloom aftervulcanization at a temperature of 320 F. for 15 minutes. Co pound Bexhibited no bloom whatsoever.

Other formulations .coming within the scope of this invention are thefollowing:

Although the present invention has been described with reference to thespecific details of certain embodiments, it is not intended that suchembodiments shall be regarded as limitations upon the scope of theinvention except insofar as included in the accompanying claims.

What is claimed:

1. A vulcanizate of a copolymer containing 70 to 99 percent by weight ofisobutylene and 30 to 1 percent by weight of a diolefin, a siliceousreinforcing pigment, 0.5 to 1.5 parts by weight of elemental sulphur,and up to 2.5 parts by weight of a dimorpholine polysulfide per 100parts by weight of the copolymer.

2. The vulcanizate of claim 1 wherein the siliceous reinforcing pigmentis finely-divided silica.

3. The vulcanizate of claim 1 wherein the siliceous reinforcing pigmentis finely-divided calcium silicate.

4. The vulcanizate of claim 1 wherein the siliceous reinforcing pigmentis finely-divided sodium aluminum silicate.

5. The vulcanizate of claim 1 wherein the siliceous reinforcing pigmentis finely-divided sodium calcium aluminum silicate.

6. The vulcanizate of claim 1 wherein the siliceous reinforcing pigmentis finely-divided aluminum silicate.

7. A vulcanizate of a copolymer containing 70 to 99 percent by weight ofisobutylene and 30 to 1 percent by weight of a diolefin, a siliceousreinforcing pigment, 0.5 to 1.5 parts by weight of elemental sulphur,and up 5 to 2.5 parts by weight of 4,4 dithiodimorpholine per 100 partsby weight of the copolymer.

8. The rubber of claim 7 wherein the copolymer contains about 97.5 partsby weight of isobutylene and 2.5 parts by weight of isoprene.

9. A method of preparing a synthetic rubber which comprises compoundingtogether a copolymer containing 70 to 99 percent by weight ofisobutylene and 30 to 1 percent by weight of a diolefin, a siliceousreinforcing pigment, and 0.5 to 1.5 parts by weight of elementalsulphur, and up to 2.5 parts by weight of a dimorpholine polysulfide per100 parts of the copolymer, and vulcanizing the resulting compoistion.

10. The process of claim 9 wherein the copolymer contains 97.5 parts byweight of isobutylene and 2.5 parts by weight of isoprene.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Wolf: Rubber Age, June 1954, pages 389-395.

1. A VULCANIZATE OF A COPOLYMER CONTAINING 70 TO 99 PERCENT BY WEIGHT OFISOBUTYLENE AND 30 TO 1 PERCENT BY WEIGHT OF A DIOLEFIN, A SILICEOUSREINFORCING PIGMENT, 0.5 TO 1.5 PARTS BY WEIGHT OF ELEMENT SULPHUR, ANDUP TO 2.5 PARTS BY WEIGHT OF A DIMORPHOLINE POLYSULFIDE PER 100 PARTS BYWEIGHT OF THE COPOLYMER.